There are three major classes of biopolymers, nucleic acid, proteins and carbohydrates. Protein and nucleic acid structure and interactions have been extensively studied in the art and the template-driven nature of protein and nucleic acid synthesis and the fact that these polymers are linear has meant that the techniques for their production and study have now been largely automated.
However, carbohydrates and their interactions with other species are also extremely important biologically and have not been the subject of concerted study. The difficulty in studying carbohydrates and their interactions arises in view of the diversity of carbohydrate linkages and because there are no techniques analogous to cloning to amplify and modify carbohydrates. On the contrary, the complex multistep way in which carbohydrates are assembled in cells means that carbohydrates and associated glycoconjugates such as glycoproteins and glycolipids are characterised by a high degree of variability and are not trivial to synthesise or study. In addition, carbohydrate mediated interactions tend to be weak and polyvalent and are correspondingly difficult to detect. Thus, there are no satisfactory tools for doing this in the art.
However, despite these characteristics, carbohydrate mediated interactions are important biologically. The surfaces of most types of cells are covered with a dense coating of glycoconjugates given rise to the so-called glycocalyx. It is believed that the glycocalyx is responsible for the repulsive forces which prevent non-specific adhesion of cells. However, in some cell configurations the repulsive barrier will be counterbalanced by the formation of cell-cell contacts through attractive forces. [1] There is now evidence that beside the well-known carbohydrate-protein interactions, [2] cells use attractive interactions between surface carbohydrates as a novel mechanism for cell adhesion and recognition. [3] A characteristic feature of these interactions is its low affinity that is compensated by a polyvalent presentation of ligands and receptors at the cell surfaces. [4]
Investigations into polyvalent carbohydrate-protein interactions have been approached using different multivalent carbohydrate model systems. [5] Examples of prior art approaches include the use of two dimensional arrays of glycoconjugates on gold surfaces [6a], the use of liposomes to display carbohydrates, dendrimer technology, and the use of polymers to provide linear and spherical carbohydrate arrays [5a, b]. However, the problems of studying interactions involving carbohydrates are far from solved and there is a continuing need in the art for new methods and tools for doing this.